Double Refraction of Quartz. 2 05 



ray. For instance, with a right-handed plate of thickness 0,38 

 inch, and using a red glass, the first red ring was rendered am- 

 biguous (if I may use that term to denote the state when the 

 ring is broken in such a manner, that it is difficult to say 

 whether the part on one side is most nearly connected with the 

 extenor or interior part on the other side) by supplying an or- 

 dinary iay only, with elliptical light, whose 



minor axis 



n7ajoTix¥ = tan17 - 15>: 



or by supplying an extraordinary ray only with light, whose 



minor axis 



^ajoTltxi^ - tan 16 °- 2 ■ 



With a left-handed plate of thickness 0,16 inch, the first red ring 

 was rendered ambiguous by supplying an ordinary ray only with 

 elliptical light, whose 



minor axis 



: = tan Q° Q' 



major axis » • *, 



or by supplying an extraordinary ray only with light whose 



minor axis 

 EajoFS = tan 8 • 50 - 



The first result is the mean of 8 measures of each, and the 

 second the mean of 4 measures*. The zero points of the rhomb- 

 graduation were determined by observing when the rings of calc 

 spar were not broken. This determination is very accurate; but 

 ■f -t were faulty, the effect of any error in the zero point, as 

 well as of any imperfection in the construction of the rhomb 



of tbe™i 'IT ^ , th<! T T S ' (by 3 r ° U « h ™«0> the rays made with the axis 

 the crystal, the angle 9°. 42' in air: and in the latter 13". 50' in air. 



